JP2786204B2 - Band stop filter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a band rejection filter used for a communication device in a microwave band.

2. Description of the Related Art Conventionally, a band rejection filter used in a microwave band is configured by connecting a plurality of series resonance circuits using a 1/4 wavelength coaxial cable.

By the way, in the band rejection filter, the insertion loss on the high frequency side or the low frequency side of the rejection frequency band is often emphasized. Next, the reason will be described using an antenna duplexer as an example.

An antenna duplexer is used for mobile radio equipment and the like. In this antenna duplexer, a transmission filter is generally connected at a terminal portion of the same antenna, and a signal from the transmission side to the reception side is prevented from being transmitted. To prevent the transmission (or reception) filter's rejection frequency band is received (or transmitted)
It is set wider than the pass band of the filter for use.
In recent years, in particular, the transmission frequency band for transmission and reception has been widened with the increase in the number of communication channels, and the pass bands for both have been approaching each other. As a result, the difference between the band edge of the pass frequency band and the band edge of the stop frequency band in the transmission and reception filters is reduced, and it is becoming difficult to satisfy both characteristics. To solve this problem, it is necessary to reduce the stop frequency band or improve the insertion loss on the high frequency side (pass frequency band) even at the expense of the symmetry of the frequency characteristic.

In order to realize the above filter characteristics,
As described in JP-A-56-79502, the distance between a plurality of series resonant circuits is set to 5
There is a method of connecting with a coaxial cable that is long (or short) by about 20%. The band rejection filter having this structure has an asymmetrical frequency characteristic, and is characterized in that the insertion loss in the low band or the high band with respect to the center frequency can be reduced.

However, since the band rejection filter as described above connects each series resonator using a coaxial cable, an increase in material cost, an increase in working time in the processing and assembly process, Further, a space for routing the coaxial cable is required, which causes a new problem of an increase in product size.

An object of the present invention is to solve the above problems and to provide a small-sized and low-cost band rejection filter.

Means for Solving the Problems In order to solve the above problems, a band rejection filter of the present invention comprises a plurality of coaxial resonators, and a central conductor of the plurality of coaxial resonators respectively provided to the plurality of coaxial resonators. A first capacitor having one end connected to the plurality of coaxial resonators and a gap provided between the plurality of coaxial resonators, and one end connected to the other end of the first capacitor, and one of the second capacitor and the inductor connected to a conductor pattern. And a substrate formed by: connecting the conductor pattern of the substrate and the other end of the first capacitor, thereby connecting the first capacitor to one of the second capacitor or the inductor, The first
And the substrate are separate members.

Operation With this configuration, a large-capacity first capacitor can be used, and replacement of the first capacitor is facilitated. Further, variation in the capacity of the first capacitor can be suppressed.

FIG. 1 is a diagram showing a first embodiment of a band rejection filter according to the present invention.

In FIG. 1, reference numerals 1, 2, and 3 denote coaxial resonators having a short-circuit portion at one end. In this embodiment, a central conductor 5 and an external conductor are provided on a cylindrical ceramic dielectric 4 as shown in FIG. 6
And the short-circuit surface 7 is formed.

Incidentally, the coaxial resonator has a rectangular cross section,
Alternatively, a material whose characteristic impedance changes in the coaxial resonator (for example, a material whose outer diameter of the ceramic dielectric 8 changes in the middle as shown in FIG. 3) may be used.

One end of a first capacitor 9, 10, 11 is connected to the center conductor 5 of the coaxial resonators 1, 2, 3 and the other end is connected via an inductor or a second capacitor formed on a substrate 12. Neighbors are connected. The outer conductors of the adjacent coaxial resonators 1, 2, 3 are connected via a conductor layer such as solder. 13 and 14 are input / output terminals used for connection to a circuit.

As the substrate 12, a substrate having a conductor pattern as shown in FIGS. 4 and 5 formed on an insulating substrate was used.

FIG. 4 shows an example in which an inductor is formed on an insulating substrate. As the insulating substrate, it is desirable to use one having a low dielectric constant or high magnetic permeability. In this embodiment, a glass epoxy substrate is used, and The copper foil adhered was etched to form a conductor pattern. As another substrate material, a Teflon or ferrite ceramic substrate or the like may be used.

FIG. 5 shows an example in which a capacitor is formed on an insulating substrate. It is desirable to use a substrate having a low magnetic permeability or a high dielectric constant as the insulating substrate. In this embodiment, an alumina substrate is used, and an Ag-Pd
The conductive material was screen-printed to form a conductor pattern.

The frequency characteristic of the band rejection filter having the above-described configuration becomes asymmetric, and when the substrate including the inductor shown in FIG. 4 is used as the substrate 12, the insertion loss in the low band side is reduced, The band-side attenuation characteristic becomes steep.

Similar results can be obtained by using an inductor obtained by processing a copper wire or the like into a coil shape or a wavy shape, in addition to the inductor formed on the substrate.

Further, the substrate constituting the capacitor shown in FIG.
In the case where the inductor is used as described above, the insertion loss on the high frequency side is reduced contrary to the configuration of the inductor as described above, and the attenuation envoy on the high frequency side becomes steep.

The product size of the band rejection filter obtained as described above can be significantly reduced as compared with the conventional one.

Capacitors 9, 10, and 11 are coaxial resonators 1, 2, and 3
By using a member different from 12, the capacitance of the capacitors 9, 10, 11 can be increased, so that the attenuation can be increased, and the filter characteristics can be improved.

Furthermore, the capacitors 9, 10, and 11 are connected to the coaxial resonators 1, 2, and 3 and the substrate.
If a defect occurs in the capacitors 9, 10, and 11 by using a member different from 12, the replacement is easy, so that repair and the like are easy to perform.

Furthermore, since the connection between the capacitors 9, 10, 11 and the center conductor 5 is easy, mounting errors and the like are less likely to occur, and the variation in capacitance caused by the connection errors can be suppressed. By providing 11, the variation in the capacitance of the capacitor itself can be suppressed, so that the filter characteristics do not deteriorate.

As described above, the band rejection filter of the present invention includes a plurality of coaxial resonators, and a center conductor and one end of the plurality of coaxial resonators connected to the plurality of coaxial resonators, respectively. A first capacitor provided with a gap between the plurality of coaxial resonators; and a substrate connected to the other end of the first capacitor and having one of a second capacitor and an inductor formed of a conductor pattern. Connecting the conductor pattern of the substrate and the other end of the first capacitor to connect the first capacitor to one of the second capacitor and the inductor, and connecting the first capacitor to the first capacitor. Since the substrate is a separate member, a large-capacity first capacitor can be used, so that the amount of attenuation can be increased, the filter characteristics can be improved,
In addition, since the first capacitor can be easily replaced, repair and the like can be easily performed. Further, the variation in the capacitance of the first capacitor itself can be suppressed, so that the deterioration of the filter characteristics can be suppressed.

[Brief description of the drawings]

FIG. 1 is a side view of a band rejection filter according to one embodiment of the present invention, FIG. 2 is a cross-sectional view of a coaxial resonator used in the embodiment,
FIG. 3 is a cross-sectional view of another coaxial resonator, FIG. 4 is a plan view of a substrate forming an inductor, and FIG. 5 is a plan view of a substrate forming a capacitor. 1,2,3 ... coaxial resonator 4,8 ... ceramic dielectric, 5 ... center conductor, 6 ... outer conductor, 7 ... short-circuit surface, 9,10,11 ... capacitor, 12 ... Substrates, 13,14 ... I / O terminals

Continuing on the front page (72) Inventor Shinichiro Ito 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 72) Inventor Hiromitsu Taki 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Moriichi 3-10-1, Higashi-Mita, Tama-ku, Kawasaki City, Kanagawa Prefecture Inside Matsushita Giken Co., Ltd. References JP-A-61-208902 (JP, A) JP-A-61-69202 (JP, A) JP-A-58-155102 (JP, U)

Claims (2)

(57) [Claims] 1. A plurality of coaxial resonators, and a center conductor and one end of the plurality of coaxial resonators are respectively connected to the plurality of coaxial resonators, and a gap is provided between the plurality of coaxial resonators. And a substrate connected to the other end of the first capacitor and having one of a second capacitor and an inductor formed of a conductor pattern. The first capacitor includes a conductor pattern of the substrate and the first capacitor. By connecting the other end of the capacitor, the first capacitor is connected to one of the second capacitor and the inductor, and the first capacitor and the substrate are separate members. Band stop filter. 2. A band rejection filter according to claim 1, wherein a coaxial resonator whose characteristic impedance ratio changes within the resonator is used.